1. Field of the Invention
The present invention relates generally to an injection molding apparatus, and more particularly to an actuator for controlling flow of molding material in a hot runner.
2. Related Art
A typical injection molding apparatus includes a runner that delivers heated molding material (melt) from a plasticizing screw to one or more mold cavities. The runner is typically an enclosed channel defined by a manifold and one or more nozzles. When the runner is heated, so as to prevent melt from freezing within the runner, it is called a hot runner.
Actuators are used with hot runners to control the flow of heated molding material. Such actuators are commonly hydraulic, pneumatic, or electric, each of which having advantages and drawbacks. Regardless of the type of actuator, the operation principle is the same, namely, to convert pressure or electricity to movement of valve pins or other flow controlling devices.
Hydraulic actuators are common, and these tend to deliver high force for their size. They also require hydraulic fluid or oil to operate, and leaks can result in contamination of equipment or environment.
Pneumatic actuators are common as well, and are cleaner in operation than hydraulic actuators. However, the compressibility of air lends itself to problems in this kind of actuator.
Electric actuators are increasingly common in hot runner applications. They are clean and can be highly accurate. However, for the same force delivered, electric actuators tend to be bulky compared to hydraulic and pneumatic actuators.